How to handle the WCF service until it Completed the Task

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Windows

phone

I have WCF service and I am utilizing that service in Windows phone 8 like below.

here i need to wait the Main thread upto when WCF service task is completed .

{
Objclinet.UserAuthenticationCompleted +=  new EventHandler<MobileServiceReference.UserAuthenticationCompletedEventArgs>(EventUserAuthenticationCompleted);
             Objclinet.UserAuthenticationAsync(ID,PWD);


}

  private  void EventUserAuthenticationCompleted(object sender, MobileServiceReference.UserAuthenticationCompletedEventArgs e)
        {
            var empobj = JsonConvert.DeserializeObject<Employeinfo_2>(e.Result);
           
           // exitEvent.Set();   

        }